In rats of the RCS type afflicted with hereditary retinal degeneration (dystrophy) visual capacities survive to a surprising degree when the great majority of visual cells has died while surviving visual cells which are mainly cone cells, have lost their sensory organelle (outer and inner segment). Survival of function has been measured in the laboratory of the Principal Investigator by the Impulsive activity of retinal ganglion cells and lateral geniculate body, by the synchronous mass responses of the primary visual cortex following flass, flicker and pattern reversal stimulation, and by the ability of the rat to discriminate between a vertical and horizontal bar. The survival of these functions is age-dependent; it slowly disappears as the rat grows older and it becomes minimal at the age of 1 1/2 years. The age-dependent decone is associatred with a decrease in the number of the remnant cone cells which becomes critical in the absence of the outer segments when 50% of the normally available cone cells has disappeared. It is planned to continue the previous study primarily with the aims of (a) to identify the photoreceptive elements by electrophysiological and histochemical means (b) to analyze changes in receptive field organization and ganglion cell responsiveness in relation to the continuous loss of photoreceptive elements and (c) to determine the role of environment light and of the pigment epithelium in the age-dependent decline in order to explore whether or not the late decline in function is a primary expression of the gene mutation. It is the long-term objective of the studies to discover means which prolong survival. The rat retina at an advanced stage of degeneration is considered a model for the pathology of the peripheral retina in human retinitis pigmentosa and related disorders.